1. Field of the Invention
The present invention relates to a muffler for use with an internal combustion engine and, more particularly, to a multi-layer tube of the muffler and a method of producing the same.
2. Description of the Prior Art
A tube of a muffler for use with an internal combustion engine is susceptible to corrosion on both the inner and outer surfaces thereof. Specifically, corrosion of the inner surface is caused by chemical reactions with water condensed in and entrained by exhaust gas and with a catalyst adapted for exhaust emission control, while corrosion of the outer surface is brought about by briny air, high humidity and other environment conditions under which a muffler is often used. That is, the cause of corrosion differs from the inner surface to the outer surface of the tube.
There has been proposed a tube for an automotive muffler having a plurality of concentric layers which are individually made of particular materials matching the different causes of corrosion as stated above, as disclosed in Japanese Patent Laid-Open Publication No. 83622/1982. The prior art multi-layer muffler is produced by laying a sheet of stainless steel on a sheet of aluminum-plated steel and, then, directly rolling the two sheets together. In detail, such a muffler is produced by winding the two sheets made of different materials at least one turn by rolling. The production, therefore, requires a considerable compression force for winding which has to be implemented with a highly rigid rolling machine. Further, it is necessary for the two blanks to be positioned with extreme care so as not to be dislocated relative to each other.